Scratching my head (extraction operator)

[bobafett]

Hi guys,

Im attempting to write(overload) an extraction operator for a class. It works fine and the fail bit is setting correctly when there is an error in the stream.

My problem is that a requirement of this operator is to leave the stream unaltered if an error in the stream is detected. That means that I can't touch the stream (ie can't put characters back into the stream etc).

I was thinking that it is possible to make a copy of the stream and manipulate it that way, and if no errors are present then I can flush the stream at the end. The only problem with this is that I have no idea how to copy the stream without actually flushing it. If anyone can help me out it would be greatly appreciated.

Thanks.

[helios]

You can't copy streams. The copy constructors are private.

Use get() while saving the return values in a stack until you encounter an error or succeed. If you encounter an error, putback() the contents of the stack into the stream.

[bobafett]

Is there a good guide to doing this? I'm not 100% confident with stacks.

[helios]

Uh... Huh?

std::stack<int> stack;
for (int a=0;a<10;a++)
    stack.push(a);
while (!stack.empty()){
    std::cout <<stack.back();
    stack.pop();
}